The temperature oscillation of the heated water at the atmospheric pressure in the test loop where the ability to remove the heat was limited had been investigated. The flow instabilities were also visually observed. The results obtained from the study suggested that there were two frequencies for the temperature oscillation, which were affected by the heat flux applied to the system. By FFT analysis, these two major frequencies temperature oscillation were then identified. For the higher heat flux, the low frequency for the temperature oscillation was resulted since the hot water spilt into the condenser section. On the other hand, only the high frequency temperature oscillation next to the location of the heater section was then observed if the heat flux was low.
